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Table of Contents
Why Is the Park Range Colorado’s Snowfall Capital? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Wolf Creek Pass 1NE Weather Station Closes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Climate in Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
October 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Colorado
Climate
Winter 2001-2002
Vol. 3, No. 1
Cover Photo: Group of
spruce and fir trees in
Routt National Forest near
the Colorado-Wyoming
Border in January near
sunset. Photo by Chris
Hiemstra, Department
of Atmospheric Science,
Colorado State University.
If you have a photo or slide that you
would like considered for the cover
of Colorado Climate, please submit
it to the address at right. Enclose
a note describing the contents and
circumstances including location and date it was taken. Digital
photographs can also be considered.
Submit digital imagery via attached
files to: odie@atmos.colostate.edu.
Unless otherwise arranged in
advanced, photos cannot be returned.
November 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
December 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Water Year in Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Why Is It So Windy in Huerfano County? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
The Cold-Land Processes Field Experiment: North-Central Colorado . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Roger A. Pielke, Sr.
Professor and State Climatologist
Nolan J. Doesken
Research Associate
Odilia Bliss, Technical Editor
Colorado Climate Center
Department of Atmospheric Science
Fort Collins, CO 80523-1371
Phone: (970) 491-8545
Phone and fax: (970) 491-8293
Colorado Climate publication (ISSN 1529-6059) is published four times per year, Winter, Spring,
Summer, and Fall. Subscription rates are $15.00 for four issues or $7.50 for a single issue.
The Colorado Climate Center is supported by the Colorado Agricultural Experiment Station
through the College of Engineering.
Production Staff: Clara Chaffin and Tara Green, Colorado Climate Center
Barbara Dennis and Jeannine Kline, Publications and Printing
An earlier publication with the same name, Colorado Climate, was published monthly from 1977 through 1996 with the
support of the Colorado Agricultural Experiment Station and the Colorado State University College of Engineering.
Web: http://climate.atmos.colostate.edu
ii Colorado Climate
Why is the Park Range Colorado’s Snowfall Capital?
Matthew D. Parker, University of Nebraska-Lincoln
M
ost Coloradans who have clicked into
a set of ski bindings are aware that
Wolf Creek Ski Area, located on Wolf
Creek Pass in the San Juan mountains
of southern Colorado, advertises “The most snow in
Colorado.” However, most Coloradans are not aware
that, on average, the most winter precipitation in the
state falls not at Wolf Creek Pass or in the San Juans,
but in the Park Range which rises up just east of
Steamboat Springs in north-central Colorado (Figs. 1
and 2). This may seem surprising in light of the fact
that the Park Range is not among the tallest mountain
ranges in the state, and does not lie within one of the
larger massifs of high terrain in Colorado (Fig. 2).
This article explores some reasons why a) the Park
Range, on average, receives the most winter precipitation in Colorado, and b) the San Juan Range periodically experiences incredibly large winter precipitation
amounts, but does not surpass the Park Range in
annually averaged precipitation.
Orographic precipitation
In the atmosphere, clouds and precipitation
generally form when moist air (air with a high relative
humidity) ascends. As the moist air ascends, it cools;
if the air cools to a sufficient degree, water vapor in
the air is condensed or deposited onto small particles
in the atmosphere, thereby forming water droplets or
ice crystals (clouds). These droplets and crystals, in
turn, can grow and coalesce with one another, eventually becoming quite large and falling from clouds as
precipitation.
Precipitation occurs in Colorado’s mountains
throughout the year. On many days during the summer
months, mountains act as elevated heat islands in
the atmosphere, producing relatively warm, buoyant
air that ascends to form a thunderstorm. However,
a preponderance of the precipitation in Colorado’s
mountains falls during the winter months, between
mid-November and mid-May. Most of the winter precipitation episodes in Colorado’s high country occur
not because buoyant air is ascending on its own, but
rather because moist air is forced up the slopes of the
mountainous terrain. Rain or snow generated by the
mountains in this way is called orographic precipitation.
Average Annual Precipitation
LEGEND (IN INCHES)
Under 10
10 to 15
15 to 20
20 to 25
25 to 30
30 to 35
35 to 40
40 to 45
45 to 50
50 to 55
Above 55
Period: 1961-1990
Figure 1: Annually average precipitation for Colorado (in inches).
This map is a plot of 1961-1990 annual average precipitation contours from
NOAA Cooperative stations and (where appropriate) USDA-NRCS SNOTEL
stations. Christopher Daly used the PRISM model to generate the gridded
estimates from which this map was derived; the modeled grid was approximately
4x4 km latitude/longitude and was resampled to 2x2 km using a Gaussian filter.
Mapping was performed by Jenny Weisburg. Funding was provided by USDANRCS National Water and Climate Center. 12/8/97
COLORADO
Large annual winter precipitation in
Colorado’s Park Range
Comparatively moister air
In order to have orographic precipitation in the
Colorado mountains, moist air must flow up against
and ascend the high terrain. Because the prevail(continued on page 2)
Figure 2: Topographic map depicting the major mountain ranges of Colorado.
The Park Range and San Juan Range are labeled, as well as locations referred to
in this article.
Colorado Climate 1
Colorado’s Snowfall
Capital (continued from page 1)
Figure 3: Surface elevation (in meters) of the western United States, with the
mean middle tropospheric streamlines for November-May shown as white
arrows.
Figure 4: Surface elevation (in meters) of the western United States, with middle
tropospheric streamlines from 26 January 2001 shown. This pattern is typical for
large snows in Colorado’s San Juan Range.
2 Colorado Climate
ing winds in the middle and upper troposphere over
Colorado are west-northwesterly (from the west-northwest), the predominant moisture source for winter
orographic precipitation in Colorado’s high country
is the Pacific Ocean (Fig. 3). From Fig. 3, it is evident
that there are several major mountain ranges upstream
from Colorado, particularly California’s Sierra Nevada
range, Utah’s Wasatch range, and Wyoming’s Teton/
Wind River/Absaroka complex. As moist air flows up
each successive mountain range, some of its humidity
is left behind as precipitation that falls out. Accordingly, the fewer mountain ranges that air must pass
over, the greater amount of humidity that remains at its
final destination.
Skiers and snowboarders have perhaps noticed
the symptoms of this phenomenon when comparing
annual resort snowfall totals in Colorado (typically
around 300 inches) to those in California, Utah, and
Wyoming (often exceeding 400 inches). On average,
airflow in the middle troposphere follows the white
streamlines in Fig. 3, arriving in the Sierra Nevadas,
Wasatch, and Wyoming mountains without having
previously spent part of its humidity by ascending
another large mountain range. The same cannot be
said for most of Colorado, which lies in the “shadow”
of the California, Utah, and Wyoming mountains. By
the time moist air from the Pacific arrives in Colorado,
it has already lost a fair amount of its initial water
vapor because it precipitated over the upstream ranges.
Notably, however, there is a gap of relatively low
terrain separating the Wasatch range of Utah from the
Teton/Wind River/Absaroka complex in Wyoming.
From Fig. 3, it becomes clear that air following the
mean streamlines through this gap will likely flow up
against the northern Colorado mountains; in particular,
the Park Range will receive the brunt of this still-moist
Pacific air. So, for the averaged winter winds, the Park
Range – unlike most of the Colorado high country – is
not in the shadow of upstream mountains, so the air
that arrives there is comparatively moist and produces
comparatively more orographic precipitation than at
other locations in the Colorado mountains.
Orientation of the range
If the ridge of a mountain range is perpendicular
to the airflow, moist air will be forced upward by the
slope of the terrain, which favors the formation of
precipitation. In contrast, if the ridge of a mountain
range is parallel to the airflow, much of the moist
air will simply flow along-side the range, not being
forced upward and hence not favoring the formation
of precipitation. For the most part Colorado’s central
mountain massif can be thought of as a north-south
barrier of high terrain (Fig. 2), which is beneficial for
orographic precipitation because it is nearly perpendicular to the prevailing west-northwesterly winter
winds (Fig. 3). The Park Range not only helps to
compose the north-south Colorado mountain massif,
but itself is also oriented roughly north-south (Fig. 2).
Accordingly, not only does especially moist air flow
into the Park Range (as described above), but it is
also forced up dramatically because the Park Range is
roughly perpendicular to the airstream. The orientation of the Yampa River Valley and the higher ground
north and south of the valley also help funnel moist air
towards the Park Range.
For the averaged winter west-northwesterly
winds, no other location in Colorado enjoys such a
favorable superposition of comparatively moist air
(owing to the Park Range’s location with respect to the
upstream terrain) and orientation (nearly perpendicular
to the mean flow).
Winter precipitation in Colorado’s
San Juan Range
The air streams shown in Fig. 3 are averaged
over the entire winter snowfall season (November
through May). However, large temporary deviations
from this average happen throughout the season.
Occasionally, when strong storms develop along the
west coast of the U.S., a highly curved airflow pattern
occurs in which Wolf Creek Pass and the San Juans
receive tremendous amounts of snowfall. You may
have noticed on Fig. 3 that there aren’t any large, high
mountain massifs to the southwest of Colorado. This
suggests that, if a southwesterly (from the southwest)
airstream could occur over the western United States,
moisture from the Pacific Ocean and Gulf of California could flow into Colorado and rise up the San Juan
range without having had to ascend over much high
terrain upstream. Furthermore, the southern edge of
the San Juan range extends roughly from northwest to
southeast (from the vicinity of Durango southeastward
toward Santa Fe, New Mexico, see Fig. 2). Therefore,
a moist southwesterly airflow would be forced to
rapidly ascend the steep southwest-facing (flow-perpendicular) slopes of the San Juans. In such a situation
the San Juan range, and particularly Wolf Creek Pass,
enjoys a juxtaposition of advantages similar to that
described above for the Park Range. One example of
this, in Fig. 4, occurred on January 26, 2001; approximately 20 inches of snow fell at Wolf Creek Pass in 24
hours from this airflow regime. Some of Colorado’s
largest single-day snow totals are received in the
San Juan Range when the atmospheric flow pattern
produces southwesterly winds across the western U.S.
For this reason, Wolf Creek Ski Area is renowned for
its deep powder skiing.
The Park Range versus the San Juan
Range: A study in variability
The difference between the annually averaged
precipitation totals for the Park Range and the San
Juans has to do with the magnitude of typical snow
events and the frequency with which they occur.
Snowfall totals for individual storms in the San Juan
Range tend to be large, but the annual snowfall totals
in this range are quite variable. The frequency with
which snow occurs in the San Juans varies widely
from month to month and from year to year because of
the special pattern needed to produce big snow events
there (Fig. 4). In some years, moist southwesterly
airflow patterns are scarce and annual snowfall totals
in the San Juan Range are extremely low, even though
one or two events in that year might produce very
large daily totals. In other years, moist southwesterly
airflow patterns are abundant, and the San Juan Range
leads the state in annual snowfall by a healthy margin.
By contrast, snowfall in the Park Range is much less
variable. Over the course of most winters, the mean
flow pattern shown in Fig. 3 prevails for much of the
season. Unlike the San Juans, the Park Range does
not receive many prolific single-day snows; however,
snow falls more regularly throughout the winter and
is more consistent from winter to winter in the Park
Range because the average winter airflow pattern is
favorable for it. In fact, not only does the Park Range
lead Colorado in average annual precipitation, but it
is also less variable from year to year than anywhere
else in the state. Accordingly, if you had to book a ski
vacation one year in advance, you might consider the
reliability of large annual snowfall in the Park Range
(i.e. Steamboat) to be very attractive; however, if you
wished to ski in waste-deep snow and could leave at a
moment’s notice, the San Juan Range might be a better
choice.
On January 26, 2001,
about 20 inches of
snow fell at Wolf
Creek Pass.
About the author: Matt
Parker was a graduate
student in the Department
of Atmospheric Science
at Colorado State from
1996-2002, during which
time he completed his M.S.
and Ph.D. degrees and
developed a fondness for
Colorado’s snowy slopes.
He is now an assistant
professor of meterology/climatology at the University
of Nebraska-Lincoln.
Colorado Climate 3
Wolf Creek 1E Weather Station Closes
Colorado Climate Center Staff
W
e regret to inform you that the Wolf
Creek Pass 1E weather station closed
November 30, 2001. This station has
been a cooperative station for the
National Weather Service taking temperature and
precipitation data since December 12, 1957. The personnel of the Colorado Department of Transportation
(CDOT) supported it. They actually lived year round
at East Side Camp at an elevation of 10,640 feet. This
location is 1 mile east of the summit of Wolf Creek
Pass. This station began as a replacement for an earlier
Wolf Creek Pass 1E
Precipitation and Temperature Averages, 1957-2001
Wolf Creek Pass 1E
Average Snowfall and Snowdepth Averages, 1957-2001
4 Colorado Climate
cooperative station that was four miles west of Wolf
Creek Pass. Because there are not many high elevation
stations in the cooperative program, losing this station
is what makes it so difficult.
Over the years many CDOT employees have
helped take weather observations, but the most recent
observer, Daniel Goldsberry, has been enthusiastically
taking weather observations since March 1990. He
and his wife, Linda, did an exemplary job for the past
twelve years taking quality observations in a difficult
and challenging environment. Thank you so much for
your time and commitment!
As we say goodbye to the Wolf Creek Pass 1E
station, we thought we would share with you some of
what we learned in the past 44 years.
Wolf Creek Pass 1E holds the state record for the
most snowfall during a winter season – a whopping
837.5 inches during the winter of 1978-79 (a heckuva
way to end the drought of 1974-77).
Some other highlights include:
1. Warmest day on record was 80°F on June 28,
1990 and July 6, 1989.
2. Coldest minimum temperature was -40°F on
February 5, 1982.
3. During the winter of 1992, Wolf Creek Pass
enjoyed a very mild winter while only a short distance
east, Alamosa and the San Luis Valley suffered
through one of their coldest winters on record. There
were 29 days that winter when Alamosa was at least
20 degrees F colder than Wolf Creek Pass. On January
3, 1992 Wolf Creek Pass 1E had a high of 39°F and a
low of +14°F. That same day in Alamosa the high was
+2°F and the low was -27°F.
4. During the late summer, moist air moves up
from old Mexico as a part of the “Southwest Monsoon” wind circulation. As a result, very heavy rains
are possible. During August of 1993, 10.89 inches
of rain fell. September 1970 brought 11.25 inches
and 14.45 inches of rain and wet snow came down in
October 1972.
Colorado Climate in Review
October 2001
Climate in Perspective
October brought a little bit of everything. There
were some very hot days early in the month. There
were some thunderstorms with hail and strong winds.
There were some heavy rains and a few heavy, wet
snows. There were cloudy days and there were sunny
days. But while the weather was changeable, it was
no more so than usual. For the month as a whole,
sunny and dry weather dominated and there were more
warmer than average days than there were cool days.
by Nolan Doesken
4" accumulated near Sedgwick. The cold air
spread into the foothills and mountains on the
5th along with clouds and a little snow while
western Colorado remained mild and dry. Skies
cleared on the 6th as the cold air mass retreated
quickly to the east.
> 100%
Precipitation
Precipitation fell somewhere in Colorado on
nearly half the days in October. Most precipitation
was light, however, with only two storm systems
bringing widespread rain or snow to at least half the
state. The greatest precipitation totals for the month
were observed in portions of Colorado’s northern
mountains where close to 2.5" of water content were
reported. Precipitation was least east of the mountains,
particularly east from Pikes Peak where several stations reported no measurable moisture for the month.
The majority of the state received less than half the
average October precipitation. Above average moisture
was limited to areas of western Colorado between
the Colorado and White Rivers and in northeastern
Colorado
50-100%
< 50%
October 2001 precipitation as a percent of the 1961-1990 average.
Temperature
Temperatures oscillated all month, especially east
of the mountains, as a series of autumn cold fronts
crossed the state. The hottest temperatures occurred
early in the month. Some stations in southeastern
Colorado hit 90 degrees F on the 2nd and again on the
7th. Pueblo reached the 80-degree mark on 9 days in
October. There were chilly days as well, but for the
month as a whole most Colorado weather stations
ended up warmer than average. October mean temperatures ranged from near to slightly above average
over the Eastern Plains to nearly 4 degrees F above
average in southwestern Colorado.
October Daily Highlights
1-3
4-6
A very warm air mass was in place over
Colorado on the 1st with high temperatures in
the 80s at lower elevations and a few mountain
clouds and sprinkles. Upper level northwesterly
winds increased 2-3rd, and much cooler air
reached northeastern Colorado by the 3rd. The
rest of the state remained warm and dry.
A shallow layer of much colder air surged
into eastern Colorado on the 4th accompanied
by low clouds. Rain turned to wet snow over
extreme northeastern Colorado where up to
< 0 degrees
0 to +2
degrees
> +2
degrees
October 2001 temperature departure from the 1961-1990 average, degree F.
Statewide average daily
precipitation graph(s)
(right and throughout this
article) shows relative
amounts of precipitation
for each region. Label on
each column indicates
percent of stations with
measurable precipitation
for each day.
Colorado Climate 5
7-15 Four storm systems crossed Colorado in rapid
succession. The first system on the 7th brought
cooler temperatures but only a few scattered
showers to western Colorado. At the same
time, temperatures shot up to near 90 degrees
over portions of southeastern Colorado. The
second system moved in quickly on the 8th and
crossed the state on the 9th. This storm brought
widespread rain and some high-mountain snow
to all areas west of the Continental Divide. A
few showers and thunderstorms developed east
of the mountains. The heaviest rains fell across
northwestern Colorado. More than an inch of
moisture fell over a sizeable area from Rifle,
Meeker and Craig west to the Utah border. The
10th brought chilly temperatures but a lot of
sunshine, but by the 11th the next disturbance
approached from the northwest with precipitation developing late in the day over western
Colorado. Most of the mountains picked up
1-4" of snow by midday on the 12th. Rye, on
the east face of the Wet Mountains southwest of
Pueblo, picked up 6" of wet snow. Little moisture fell east of the mountains with the exception of the Burlington area where 0.75" of rain
was reported. Very strong northwesterly winds
aloft then developed, with gusts exceeding 60
mph in the eastern foothills and high mountains
12-14th. The last in this series of storm brought
several hours of cold rain turning to snow over
northeastern Colorado while the rest of the state
remained dry. Holyoke picked up 0.53".
16-20 A dry period with seasonal temperatures but
some strong winds in the mountains.
21-23 Some moist Pacific air reached Colorado bringing valley rain and mountain snow showers.
Most showers were light but Crested Butte
totaled 0.41 inches. Eastern Colorado remained
mild, dry but windy.
24-25 Clearing and cold. The low temperature at
Antero Reservoir in South Park dipped to 5
degrees F on the morning of the 25th.
26-29 A ridge of high pressure over the Rockies
brought dry weather with above average temperatures to the state.
30-31 A Pacific storm crossed California on the
30th but only scattered rain and snow showers
remained by the time it reached Colorado on
Halloween. Strong winds were widespread,
however, and gusts exceed 70 mph in wind
prone areas of the Front Range.
Month: October 2001
Precipitation (day):
Precipitation (total):
High Temperature:
Low Temperature:
6 Colorado Climate
Shoshone, 1.42", 10/9/01
Shoshone, 2.10"
Fruita, 93°F, 10/1/01
Climax, 4°F, 10/26/01
November 2001
Climate in Perspective
A series of storms in late November brought
much needed and much appreciated snows to the
Colorado mountains. This got the 2001-2002 winter
recreation season off to a reasonably good start despite
the nation’s economic downturn and travel anxiety
resulting from the September 11 terrorist attacks. But
the first three weeks of November kept snow lovers
very nervous as extremely mild temperatures prevailed
and the only storm that hit the state brought mostly
rain.
Precipitation
November storms deposited a total of more than
four inches of water content on the Grand Mesa of
western Colorado and in other mountainous areas.
Low elevations both east and west of the mountains
also received generous precipitation. The majority of the state ended up wetter than average for the
month with substantially above average moisture in
northwestern Colorado, the western slopes of the San
Juan mountains, and over the central and northeastern plains. Holyoke totaled 1.75" of rain and melted
snow, nearly three times the average. Not all areas
benefited, however, and November ended up drier than
average over much of southern Colorado and much
below average in South Park and the Collegiate Valley
from Salida to Buena Vista. Southeastern Colorado
from Cheyenne Wells southward to Lamar and Holly
also received less than 50% of the average November
precipitation.
Temperature
Cold air with some subzero readings arrived
in late November but not before Coloradoans had
enjoyed an unusually mild November. The first three
weeks of the month were consistently warm. For the
month as a whole, temperatures ended up three to five
degree Fahrenheit above the long-term averages in all
areas of the state. With little snowcover until the last
few days of November, Crested Butte ended the month
more than six degrees above average.
November Daily Highlights
1-6
7-8
November got off to a dry and unseasonably
warm start with daytime temperatures in the
60s and 70s at lower elevations
A vigorous, moisture-laden storm brought
widespread precipitation in the form of both
rain and snow to most of Colorado. Not much
cold air accompanied the storm, so snow melted
quickly. Precipitation totals ranged from a trace
to a few hundredths over most of southern
Colorado to 0.95" at Joe’s in eastern Colorado
Montrose, Gunnison, Aspen and Crested Butte
all got over 0.50" of water content, but even in
the mountains the snow melted soon from roads
and open areas.
9-17 Nine consecutive days of unseasonably warm
and dry weather just before the Thanksgiving
holiday made for a nervous winter recreation
industry. Temperatures climbed into the 60s and
low 70s each day at lower elevations, although
clouds and cooler temperatures were reported
over southern Colorado 15-17th, as an upper
level low pressure area skirted just south of
the state. Ski area snowmaking efforts were
hampered by warm temperatures as well, with
daily highs in the 50s.
18-21 At last, a bit of a storm took aim at Colorado
on the 18th bringing cooler temperatures closer
to the averages for mid November, and a few
hours of snow (some rain east of the mountains). Most mountain weather stations reported
less than 3" – pretty puny – but Walsenburg had
4" and Climax measured 5 inches. Southwest
and northeast Colorado missed out on most of
the precipitation, and southwest Colorado continued having much warmer temperatures than
average. Precipitation ended on the 19th, but
some fog lingered. Skies cleared on the 20th
bringing the first subzero temperatures of the
winter to a few high mountain valleys. Daytime
temperatures warmed quickly, and Canon City
hit 73°F on the 20th. Mild, dry weather continued on the 21st, but clouds increased in advance
of a developing storm system along the Pacific
Coast.
22-30 Winter eased its way into Colorado as the jet
stream strengthened and moved southward
bringing a series of storms and progressively
colder temperatures to the Rockies. The first
system developed rapidly on the 22nd over
Colorado and became a very deep low pressure
area over Kansas on the 23rd. Widespread
precipitation accompanied this storm with cold
rains over portions of eastern Colorado and wet
snows in the mountains. The heaviest rainfall
total was 0.70" at the Karval station in southern
Lincoln County. 4-8" of snow was common
throughout the mountains but with more than a
foot of new snow in the southwestern mountains. The Telluride weather station west of
town picked up nearly 20" of snow with a water
content of 1.31". After a short respite on the
24th, and second storm moved in on the 25th.
This time, arctic air joined forces to help create
a dangerous situation. Substantial snows fell in
the mountains, but an area of heavy snow also
developed east of the mountains extending from
east of Denver northeastward to Akron, Yuma,
Holyoke and Julesburg. Holyoke and Julesburg both measured close to one inch of water
content from 10 inches of windblown snow.
The storm moved away from Colorado on the
26th, but cold air lingered. Subzero nighttime
temperatures were widespread in the mountain
and over portions of northeastern Colorado.
Walden, Hohnholz Ranch (Larimie River) and
Crested Butte all had low temperatures below
-20° F on the morning of the 28th. November
> 200%
150-200%
100-150%
50-100%
< 50%
November 2001 precipitation as a percent of the 1961-1990 average.
< +4
degrees
> +4
degrees
November 2001 temperature departure from the 1961-1990 average,
degree F.
Colorado Climate 7
ended with more cold and snow as yet another
storm crossed the Rockies 29-30th with several
more inches of snow. The timing of this snow
could not have been better for Colorado’s
winter recreation industry.
> 100%
50-100%
< 50%
December 2001 precipitation as a percent of the 1961-1990 average.
Month: November 2001
Precipitation (day): Hamilton, 1.55", 11/23/01
Precipitation (total): Wolf Creek Pass 1 E, 3.77"
High Temperature: Springfield 7 WSW, 86°F, 11/1/01
Walsh 1 W, 86°F, 11/1/01
John Martin Dam, 86°F, 11/1/01
Holly, 86°F, 11/1/01
Low Temperature:
Hohnholz Ranch, -21°F, 11/28/01
Walden, -21°F, 11/1/01
December 2001
Climate in Perspective
December weather patterns provided many
opportunities for significant winter snowfall. At least
eight definable storm systems approached Colorado
in the first three weeks of the month. Several were
predicted to be major snowstorms. Most storms fizzled
as they crossed the Rockies leaving only a few inches
of snow in some areas. East of the mountains, most
storms just “blew over” dropping little or no moisture.
The frequent snows and fairly cold temperatures in the
mountains provided acceptable skiing conditions for
most of Colorado’s large resorts. The water content
of the snow, however, lagged behind what would
normally be expected for early winter.
Precipitation
< -4
degrees
-4 to -2
degrees
-2 to 0
degrees
0 to +2
degrees
+2 to +4
degrees
> +4
degrees
December 2001 temperature departure from the 1961-1990 average,
degree F.
8 Colorado Climate
Despite the many opportunities, December
precipitation totals were below average over most of
Colorado. Totals exceeded three inches in the higher
elevations of the northern and central mountains
and were relatively close to average. But adjacent
valley areas were drier than average. As is often the
case during midwinter, little moisture fell east of the
mountains. Many stations in northeastern Colorado
reported less than 0.05" of water content all month.
The exception was the southeastern plains where a
few of the storms dropped some snow. Rocky Ford, La
Junta, Lamar and Walsh were wetter than average for
December, but their monthly totals were only about
0.50 inches.
Temperatures
Subzero temperatures were common in December in the mountains and high valleys of western
Colorado. Fraser dropped below zero on 22 nights
during the month. Most of western Colorado ended up
one to three degrees F below average. With fresh snow
cover, Gunnison’s temperatures were seven degrees
below the long-term average making this their coldest
December since 1978. East of the Continental Divide
was markedly warmer with most stations two to four
degrees above average.
December Daily Highlights
1-7
8-9
10-13
14-16
17-20
21-22
23-28
Dry and warm east of the mountains with
occasional gusty “downslope” winds. Near
Westcliffe in southern Colorado winds gusts of
87 mph were registered the night of December
5th. Mostly cloudy across the mountains and
western valleys with periods of snow, as mild,
moist Pacific air masses moved inland. With
fairly warm temperatures, snow accumulation
in the valleys was limited. But higher in the
mountain this was one of the snowiest weeks of
the year. Steamboat Springs totaled 9" 1-2nd.
Crested Butter piled up 8" 2nd-3rd. Aspen
reported 6" the morning of the 5th. The heaviest
burst of snow came overnight on the 6th. Vail
reported nearly a foot of new snow at their
observation on the morning of the 7th with a
water content of 1.30".
A break between storms with clearing skies.
Cold nighttime temperatures over the fresh
mountain snows. Crested Butte reported -8°F
on the 8th.
Clouds and light snow spread into Colorado
from the SW on the 10th as a low-pressure
trough approached. Low pressure developed
over the Eastern Plains on the 11th. Areas of
rain and snow developed on the 12th followed
by much colder temperatures. Burlington
measured 4 inches of snow with 0.51" of water
content. Rocky Ford picked up 6" of new snow,
but most of the plains got just a light dusting.
The storm weakened on the 13th, but cold temperatures prevailed, especially in the mountains.
Crested Butte reported a low of -24°F on the
13th.
A Pacific storm moved inland with a push of
moist air into the Rockies. Several inches of
snow fell in some areas with close to a foot of
new snow in a few exposed portions of the San
Juan mountains. The Front Range foothills also
received snow with 5" at Conifer, Evergreen
and Estes Park. Little or no snow reached eastern Colorado.
A dry period for most of the state with some
strong westerly winds aloft and just a few
mountain snow showers. Daytime temperatures
were quite warm, especially east of the mountains. Pueblo hit a high of 67°F on the 17th
after a morning low of just 12 degrees.
A fast moving storm crossed Colorado. A little
snow fell in the mountains, but parts of SE
Colorado also received beneficial moisture.
Lamar, for example received 0.30" of water
content including 2" of snow.
Dry with lots of sunshine and seasonal temperatures as a high pressure ridge remained nearly
stationary over the northern Rockies 23rd-27th.
Clouds increased on the 28th in advance of an
approaching storm.
29-31 Mild and moist Pacific air moved into western
Colorado, while a shot of arctic air moved
down from Canada into eastern Colorado. The
southern mountains picked up a few inches
of much needed snow, and the southern Front
Range also got some moisture. Walsenburg
reported 5" of fresh snow on the 30th. Most of
northern Colorado remained dry and only a few
flurries fell on the eastern plains.
Month: December 2001
Precipitation (day):
Precipitation (total):
High Temperature:
Low Temperature:
Vail, 1.20", 12/7/02
Vail, 3.03"
Campo 7 S, 79°F, 12/4/02
Crested Butte, -24°F, 12/13/02
Gunnison 3 SW, -24°F, 12/25/02
Water Year in Review
Through December 2001
The first three months of the 2002 water year left
most of Colorado with less than average precipitation.
Thanks to a few fall storms, the area from northeast
El Paso County northeast through Limon into Yuma,
Phillips and Sedgwick Counties were above average as
was a small area of northwestern Colorado. All other
areas of Colorado were dry with substantial portions
of central Colorado totaling well below 50% of the
October-December average. The driest area was Park
County with only about 25% of average. Larimer and
Boulder counties in northern Colorado, and portions
of several counties in southeastern and south central
Colorado were also far below average.
> 100%
70-100%
50-70%
< 50%
Water Year 2002 (October 2001 through December 2001) as a percent of the
1961-1990 average.
Colorado Climate 9
Stump the Climatologist
Question: Why is it so windy in Huerfano County?
Submitted by Jim Conley, Huerfano County Cooperative Extension Office
A
If you would like to
submit a question for
the Climatologists
to answer, send
it to odie@atmos.
colostate.edu
Topographic view of
Mosca Pass in the Sangre
De Cristo Mountains.
Drawing courtesy of
Christopher Hiemstra.
10 Colorado Climate
nswer: Episodic strong winds are a part of
life for all areas in the immediate lee (just
east of) the high Rocky Mountain chain.
Most of these strong winds are relatively
brief but severe associated with rapidly descending air
cascading over the crest of the Rockies and racing out
to the plains.
These “Down-Slope Wind storms” are most
common from late autumn into spring and accompany travelling upper level disturbances in the strong
wintertime jet stream. Fort Collins, Boulder, Denver,
Colorado Springs and Pueblo are all prone to these
windstorm events.
There are a few “preferred” areas that see strong
winds much more commonly. Particular topographic
features along the Front Range of the Rockies make
certain areas more prone to strong winds than others.
Portions of Huerfano County are in one of those wind
zones.
There are three topographic features of your area
that work together to produce a “wind tunnel.” A clue
to this tunnel is the location of the Great Sand Dunes.
The long, relatively straight and broad valley of the
Huerfano River happens to run parallel to the strongest
upper level winds that blow over the Rockies in the
winter. The bend in the Sangre De Cristo Mountains
(and the protruding Blanca Peak massif) channels
the winds toward Mosca Pass. Mosca Pass provides a
low pass for the concentrated winds to blow through.
Then, on the eastern side is a long, broad and straight
valley headed straight for the open plains. And thar’
she blows!
This is not a year-round wind tunnel. From late
spring through mid autumn when upper level winds
are light, the Huerfano County winds are not strong.
But as long as the upper-level “Westerlies” are blowing, your wind tunnel will often be working. One
of the benefits of these winds are markedly warmer
winter temperatures. Compare temperatures at Westcliffe to those of Gardner on a breezy winter morning.
The difference can be huge – as long as you don’t
consider the wind chill effect.
Under certain circumstances winds can reverse
and blow up the valley. When easterly “upslope”
winds blow, the Huerfano valley becomes a preferred
location for heavy snows. In the summer, upvalley
winds create preferred locations for thunderstorm
development. The wettest areas in Colorado in July
and August are often found in the Wet and Sangre de
Cristo Mountains where these upslope easterly daytime winds converge with monsoonal winds blowing
up from the south or southwest at mountain top level.
Thanks for a good question.
Nolan Doesken
The Cold-Land Processes Field Experiment:
North-Central Colorado
By Glen E. Liston, Department of Atmospheric Science, Colorado State University;
Don Cline, NOAA, NWS, National Operational Hydrologic Remote Sensing Center;
and Kelly Elder, USDA Forest Service, Rocky Mountain Research Station
Introduction
D
uring the winters of 2001-2002 and 20022003, there is a Cold-land Processes Field
Experiment taking place in Colorado
(Figure 1). This experiment is designed to
advance our understanding of the terrestrial cryosphere – cold areas of Earth’s land surface where
water is frozen either seasonally or permanently. These
areas, where snow, ice, and frozen soils and vegetation
are common, have a large influence on global water,
energy, and biogeochemical cycles. The storage of
large amounts of fresh water in seasonal snow covers
is a critical element of Earth’s hydrologic cycle. On
average, over 60% of the northern hemisphere land
surface has snow cover in midwinter, and over 30% of
Earth’s total land surface has seasonal snow.
In many high-latitude and mountainous regions of
Earth, the majority of total annual precipitation occurs
as snowfall, and snowmelt is responsible for most of
the total annual streamflow. Seasonal snow-covers
are a large energy sink in Earth’s energy cycle, and
through their effects on land surface albedo, the net
radiation balance, and boundary layer stability, have
profound affects on weather patterns over large areas.
Frozen soils also have large effects on Earth’s water
and energy cycles.
Seasonally and permanently frozen soils occur
throughout higher latitudes and at high elevations;
they are thought to occur over at least 35% of Earth’s
land surface, including approximately 50% of northern
hemisphere land areas. Seasonal and permanent frost
in soils, reduce both infiltration into and migration of
water through soils, and severely reduce the amount
of water that can be stored in soils. By reducing
infiltration, frozen soils can dramatically increase the
runoff generated from melting snow. An estimated
7.2% of the world’s organic carbon resides in the
annually thawing surface layer of tundra soils alone.
In these environments, vegetation growing seasons are
determined primarily by the thawed period. In turn,
the timing of the spring thaw and the duration of the
growing season are strongly linked to the carbon balance of seasonally frozen ecosystems. The influence
of seasonally and permanently frozen land surfaces
extends to engineering in cold regions, trafficability
for humans and other species, and a variety of hazards
and costs associated with living in cold lands.
Figure 1. Nested study areas for the Cold Land Processes Field Experiment.
The map limits depict the Large Regional Study Area (4.5 x 3.5 degrees) in
north-central Colorado and south-central Wyoming (blue boundary). The Small
Regional Study Area (2.5 x 1.5 degrees) boundaries are shown in red. Within
that area are the three 25-km x 25-km study areas: North Park, Rabbit Ears, and
Fraser. Each of these three areas contains three 1-km x 1-km Intensive Study
Areas (not shown) where most of the field observations are being collected.
Scientific Objectives
To advance our understanding of the terrestrial
cryosphere, the Cold Land Processes Field Experiment
(CLPX), largely funded by NASA, has been designed
and implemented. Complete details of the Experiment
can be found at the web site: http://nohrsc.nws.gov/
~cline. Developing a more complete understanding
of fluxes, storage, and transformations of water and
energy in cold land areas is a critical focus of the
NASA Earth Science Enterprise Research Strategy,
(continued on page 12)
Colorado Climate 11
The Cold-Land Processes Field Experiment
Figure 2. Schematic
diagram of the nested
study areas for the Cold
Land Processes Field
Experiment.
(continued from page 11)
the NASA Global Water and Energy Cycle (GWEC)
Initiative, the Global Energy and Water Cycle Experiment (GEWEX), and the GEWEX Americas Prediction Project (GAPP). The movement of water and
energy through cold regions, in turn, plays a large role
in ecological activity and biogeochemical cycles.
The Cold Land Processes Field Experiment
focuses on developing the quantitative understanding,
models, and measurements necessary to extend our
local-scale understanding of water fluxes, storage,
and transformations to regional and global scales. The
experiment emphasizes developing a strong synergism
between process-oriented understanding, land-surface
models, and remote sensing.
Quantitative understanding of cold-land processes over large areas requires the following four
major science questions to be addressed together:
1. Process Understanding. How do the extent
and evolution of snow and frozen landscapes affect
fluxes, storage, and transformations of water, energy,
and carbon?
2. Spatial Variability. At what scales does the
spatial variability of key state variables in the terrestrial cryosphere, including snow characteristics, soil
moisture, the extent of frozen soils, and the transition
between frozen and thawed conditions, control fluxes
and transformations of water, energy, and carbon, and
can remote sensing resolve this variability at these
scales?
3. Temporal Variability. What are the rates of
change of the dominant cold land processes, and can
remote sensing resolve these with sufficient accuracy
to diagnose and improve land surface models?
4. Uncertainty. How do the various uncertainties associated with remote-sensing observations and
models of cold land processes constrain/affect data
assimilation and the ability to improve forecasts?
The Cold Land Processes Field Experiment is
designed to help answer these important scientific
questions.
Experimental Design
Figure 3. Schedule for Intensive Observation Periods (IOP) for the CLPX
program, in the context of seasonal meteorologic, hydrologic, and ecological
variations.
12 Colorado Climate
The experimental design for CLPX is a multisensor, multi-scale approach to providing the
comprehensive data set necessary to address the
general science objectives of the Experiment. A set
of nested study areas, ranging from 1 ha to 160,000
km2, provides the framework necessary to permit a
detailed examination of cold land processes, modeling, and measurement over a wide range of physiographic conditions and spatial scales (Figures 1 and
2). Within this framework, intensive ground, airborne,
and spaceborne observations are being collected, and
land surface model data sets generated, to produce a
comprehensive data base sufficient to meet the science
objectives.
The experiment study sites and schedule have
been designed to efficiently provide a wide range
of snow and frozen soil, topography, and vegetation
conditions, with strong consideration given to winter
accessibility and safety issues. The experiment is
being conducted in the complex terrain of north-central Colorado (Figure 1), where elevation gradients and
slope/aspect variations provide a wide range of conditions over relatively short distances. Study sites have
been selected that range from low-relief (flat topography), unforested areas with shallow snow covers,
to high-relief (complex topography), densely forested
areas with deep snow covers. The experiment will
also exploit seasonal variations in snow and frozen
soil conditions. Field campaigns are being conducted
in late winter (mid-February), when predominantly
frozen conditions and dry snow covers are expected,
and in early spring (late-March), when transitional
(e.g., frozen and thawed) conditions and predominantly wet snow covers are expected ( Figure 3). The
field campaigns were conducted in 2002 and repeated
in 2003 (see the previously-listed web site).
Data collection during the experiment is focusing
on 1) active- and passive-microwave remote sensing observations from ground, aircraft, and satellite
platforms (Figure 4), 2) intensive in situ observations
of snow and soil characteristics (Figures 5 and 6), and
3) in situ meteorological observations.
CLPX is likely the largest and most comprehensive field experiment to be implemented with such a
major focus on snow and other cold-related processes.
The data sets collected as part of this effort are
expected to have an important impact on our understanding and ability to model and forecast weather and
hydrologic processes in cold, snowy regions such as
Colorado.
Figure 4. The NASA DC-8
on a high-altitude (39,000’
MSL) AIRSAR, POLSCAT,
and PSR flight line over
North Park. Inset, upper
left: AIRSAR antenna
(upper structure) and
PSR instrument (lower
drum-shaped instrument)
mounted on the DC-8.
Inset, lower right: NASA
flight crew at work.
(Inset-photos credit: Koni
Steffen).
Figure 5. Denny Hogan
(Colorado Avalanche
Information Center) and
Steve Muller make snow
measurements at the
Alpine Intensive Study
Area.
Figure 6. Gus Goodbody
(Colorado State
University, left) and John
Fitzgerald in a snow pit at
the Buffalo Pass Intensive
Study Area. The photo
illustrates the replicate
snow density sampling
protocol used in all CLPX
snow pits. Snow depth here
is about 2.2 meters.
Colorado Climate 13
Photo by Ian Wittmeyer, Horsetooth Reservoir.
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